TRR photo by Scott Rando

This is Walker Lake in Shohola, PA looking north. Many trees are still green or pale yellow, with a few red trees, which are probably maple. There is some fall color evident, but paler than in normal years.
 

The reason for those dull fall colors

Fall is here, and most of us have already been raking or blowing a few leaves off the driveway or walkways. A couple of things are evident with the colors of the autumn leaves this year: a lot of the leaves are still green (or took longer to change color), and the leaves that did turn color seemed to be a duller red or yellow. Those of you who have guessed that the weather played a part in this year’s less colorful fall are right, but for another reason than just mild weather. Let’s look at some leaf chemistry.

Chlorophyll is a chemical compound found in all green plants, and it gives leaves their green color. During the summer, an abundance of chlorophyll is produced by the tree. The shorter days of fall trigger plants to lessen the amount of chlorophyll produced. Chlorophyll decomposes at a constant rate, so the green starts to fade from the leaves and this  allows the other compounds, which are always present during spring and summer, to become visible.

These other compounds that provide the brilliant fall colors due to diminishing chlorophyll levels include anthocyanin, which produces the red color in the leaves of some species and needs light for production. Another major compound class is the carotenoids; they are responsible primarily for yellow colors and do not require light for production. There are many more compounds in a leaf, but this is the pair that contribute most.

Because of the abundant rainfall and overcast skies the region has experienced in the last month or so, there was less sunlight than normal. The lack of sunlight had the effect of diminishing the production of anthocyanin in the leaves (less red).

The yellow colors are still there, but they are subdued, and you might ask, “Why are many of the leaves still green?” The reason for this is that chlorophyll decomposes more rapidly with light and cool temperatures. With less sunlight from overcast skies and mild conditions, the leaves still contain enough chlorophyll for the leaf to be green (and mask the other pigments). Finally, the anthocyanin and carotenoids will also start to decompose, and with slower chlorophyll decomposition, leaves may show little or no color before turning brown.

For optimum fall color, most experts agree that a spring and summer with adequate rainfall followed by an autumn with abundant sunshine and cool nights are the best. Nature throws a curveball sometimes, and we see the results the next day, season, or even next year. Get out and enjoy the outdoors, even with a slightly muted fall coloration.

 

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